Instrument keying circuit



Aug. 21, 1962 w. H. KRUG INSTRUMENT KEYING CIRCUIT Filed June 3, 1960 aa a 2N m 2 z. c

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BY I VOLTA6 7 atet 3,049,957 Patented Aug. 21, 1962 3,049,957 INSTRUMENTKEYING CIRCUIT William H. Krug, Janesville, Wis, assignor to GihbsManufacturing & Research Corporation, a corporation of Wisconsin FiledJune 3, 1960, Ser. No. 33,847 2 Claims. (Cl. 841.09)

This invention is concerned with a keying system for an electronicmusical instrument.

Certain types of electronic musical instruments utilize tone generatingsystems which are sensitive to the supply or actuating potential for anelement of the generator, and this voltage senstivity may be utilized tocontrol the amplitude of the generated tone representing signal. Forexample, in an electronic organ utilizing photoelectric scanners fortone generation, the lamps which provide illumination for the photocelltone generators may be operated at different potentials to provide aproper balance in the amplitude of various tones generated. However,with certain stop and keying combinations, the same lamp may beenergized from voltage sources of different potential; and this has atendency to reduce the potential of the higher potential source. Theresultant reduction of the amplitude of the other tone signals actuatedby the higher potential sources is objectionable.

It is a principal object of this invention to provide a keying circuitwhich prevents interaction of this nature between power sources ofdiffering potential.

One feature of the invention is the provision, in an electronic musicalinstrument having voltage sensitive tone generating elements, of a firstpower source at one potential, a second power source at anotherpotential, switch means for selectively actuating desired tonegenerating elements from said sources, and means connected between saidsources, isolating one from the other. A further feature is that a diodeis connected with the source of lower potential isolating the source ofhigher potential from it.

Further features and advantages of the invention will readily beapparent from the following specification and from the drawings, inwhich:

FIGURE 1 is a fragmentary exploded view of a scanner tone generatingsystem;

FIGURE 2 is a schematic diagram of a circuit embodying the invention;and

FIGURE 3 is a curve illustrating the relation of lamp brilliance toapplied voltage.

In copending but abandoned Ziehlke application Serial No. 753,771, filedAugust 7, 1958, now abandoned and replaced by application Serial No.116,924, filed June 9, 1961, both assigned to the assignee of thisinvention, the details of a photoelectric cell tone signal generatingsystem are disclosed. The present invention is particularly adapted foruse with this type of tone generation. FIG- URE 1 illustrates the basicelements of such a tone generating system including a light source orlamp 10, and a mask plate 11 having a light transmitting area 12 with aconfiguration related to the tonal quality of the sound to be generated,as explained in the Ziehlke application. A scanning disc 13 is providedwith scanning slots 14 which are moved past the aperture 12 of the maskplate at a predetermined rate, controlling the repetition rate oftransmission of light to photocell 14 and the frequency of the generatedsignal. The harmonic content of the electrical signal generated inphotocell 14 is established by the configuration of mask area 12 and therelative width of scanning operations 14-. Further details of theconstruction and operation of the tone generating system may be found inthe Ziehlke application.

The amplitude of the generated signal is dependent on several variablesincluding the height of mask opening 12, the width of scanning slots 14and the light output of lamp 10. The light output, in turn, is afunction of the voltage applied to the lamp (FIGURE 3). In the tonegenerators disclosed in the Ziehlke application there are physicalconsiderations which limit the maximum size of the mask openings,particularly in the low frequency or pedal tones. Conversely, the maskopenings for the higher frequency tones cannot be reduced in size beyonda certain point Without introducing excessive noise into the generatedsignal. To provide the proper balance in amplitude between the lower orpedal notes and the higher or manual notes, a system is utilized inwhich the lamps for the pedal tones are energized from a source at apotential higher than the energizing source for the manual tones. Morespecifically, the pedal notes are energized from a ten volt circuitwhile the manual notes are energized from an eight volt circuit.However, there are certain lamps which may 'be energized from either ofthe sources, depending upon the particular stop arrangement used; andwith some conditions of stop and key switch actuation, the same lamp maybe connected with both sources. This is undesirable as the ten voltpedal source tends to drop toward the eight volt level, reducing theamplitude of other pedal tones which may be sounded.

Turning now to FIGURE 2, a circuit is illustrated which reducesundesirable effects. Two -D.C. sources are provided, the first at 20,with an eight volt potential and the second at 21, with a ten voltpotential; and both of the sources have a common positive return lead22. Connected with the source 2! is a low potential bus 20a and withsource 21 a high potential bus 21a. Four lamps 23a, 23b, 23c and 23d areshown, it being understood that a complete musical instrument will havea great many more lamps. Lamps 23a and 23b may be connected with eitherthe eight volt or ten volt bus 20a or 21a, through key switches 25 or 26and 27 or 28, respectively. Lamp 230 is connectable only with ten voltbus 21a through key switch 2 9 while lamp 23a is connectable only withthe eight volt bus 20:: through key switch 30.

Ignoring for the time being the diode 31 connected between the lowpotential terminal 20 and bus 20a, it will be seen that if either keyswitch 26 or 28 is closed connecting lamps 23a or 231) with ten volt but21a, and either key switch 25 or 27, respectively, is also closed, thetwo buses are tied directly together. As pointed out above, this tendsto drop the voltage of high potenial bus 21a reducing the brilliance ofthe lamps connected thereto and causing a reduction of amplitude of thegenerated tones.

The diode 31, connected between potential source 20 and bus 20a andpoled to conduct current only toward the potential source effectivelyisolates the higher potential source 21 from the lower potential source20; and when key switches are actuated as outlined above, the result isthat both buses shift to the higher potential. Thus, if there is anyshift in the amplitude of the generated signals it is in the directionof an increased output, rather than decreased; and this is notparticularly objectionable from a practical standpoint.

The additional loads across the low potential source include aresistance 32 representing the tube filaments of the amplitfier utilizedin the musical instrument and a solenoid coil 33, controlled by a switch34, which is a portion of the vibrato control arrangement for theinstrument.

While I have shown and described certain embodiments of my invention, itis to be understood that it is capable of many modifications. Changestherefore, in the construction and arrangement may be made withoutdeparting from the spirit and scope of the invention as disclosed in theappended claims.

I claim:

1. In an electronic musical instrument having voltage sensitive tonegenerating elements, a keying circiut for selectively actuating desiredtone generating elements: comprising a first direct current power sourceat one potential; a second direct current power source at a higherpotential; a first bus conductor connected with said first source; asecond bus conductor connected with said second source; said busconductors having the same polarity; switch means for selectivelyactuating desired elements by connecting at least some of themoptionally with the first bus, or with the second bus, or with both ofsaid bus conductors simultaneously, such that when said switch means isactuated to connect any of said elements to both of said bus conductorssimultaneously said bus conductors are connected together and have thesame potential; means connected between said first power source and thefirst bus conductor for isolating the second power source from the firstpower source to energize both of said bus conductors from said secondpower source at the higher of said potentials whenever said busconductors are connected together.

2. In an electronic musical instrument having voltage sensitive tonegenerating elements, a keying circuit for selectively actuating desiredtone generating elements: comprising a first direct current power sourceat one potential; a second direct current power source at a higherpotential; a first bus conductor connected with said first source, asecond bus conductor connected with said second source; said busconductors having the same polarity; switch means for selectivelyactuating desired elements by connecting at least some of themoptionally with the first bus, or with the second bus, or with both ofsaid bus conductors simultaneously, such that when said switch means isactuated to connect any of said elements to both of said bus conductorssimultaneously said bus conductors are connected together and have thesame potential; a diode connected between said first power source andthe first bus conductor and oriented for isolating the second powersource from the first power source to energize both of said busconductors from said second power source at the higher of saidpotentials whenever said bus conductors are connected together.

References Cited in the file of this patent UNITED STATES PATENTS2,512,639 Gohorel June 27, 1950 2,566,426 Parks Sept. 4, 1951 2,577,753Hanert Dec. 11, 1951 2,839,960 Jones June 24, 1958 2,941,434 Clark June21, 1960

